This configuration option determines whether all IDE configuration
options are always saved into a global prefs.cl
file or into a separate file for each user. The latter may be useful
when multiple users use the same lisp installation, so that each user
may use individualized options.

If nil, then options are always
saved to a file named prefs.cl in the main
Allegro directory.

If the value of the option is true (starting in release 8.0 the
default), then the path of the file that is saved depends on who is
currently logged in, and whether a unique home directory exists for
this user. If no official home directory is found for the user who is
currently logged in, or the home directory is found to be the root
directory on the C drive, then it is assumed that the current user
does not have a unique home directory, and options are saved to a file
named prefs-[username].cl in the main Allegro
directory, where [username] is the current user's login name. If a
home directory is found and is not the root directory on the C drive,
then options are saved to a file with a name similar
to allegro-prefs-8-1.cl in this home
directory; this would allow the file to be saved even if write
protection is placed on the Allegro directory. The version
number is included in the file name to avoid loading an options file
from a newer version of Allegro into an older version, which could
break on newer options. The word express will also be added to
the end of the file name in the Express version. The actual pathname
that will be used can be found by calling options-path.

The heuristic described above is intended to handle typical needs for
user-specific options files or for avoiding a write-protected Allegro
directory. If that default behavior is not adequate, then you can
specify an explicit path by setting up an environment variable called
"allegro_prefs" and whose value is the complete path namestring for
the options file. This variable will take precedence in all
cases. Example value: h:/important-files/allegro-prefs.cl. The
path's directory should already exist. Environment variables are
normally set up in the System area of the Windows Control Panel. The
string case of environment variables is not important to Windows but
Allegro CL expects lowercase so the variable name, allegro_prefs, must
be lowercase. Its value may use either forward or backward slashes.

When starting the IDE, options are always loaded from the
user-specific location if the file exists, and otherwise from
prefs.cl
in the Allegro directory if that file exists. The reason is that
options have not yet been loaded in order to determine where they were
most recently saved. Therefore, to revert from using user-specific
options files to using the global
prefs.cl file, you need to delete the
user-specific files that have been saved. Except for this, the value
of this option will be saved with the rest of the options and will
continue to be used in subsequent IDE sessions after being specified
once.

On Linux/Unix, the home directory is the value of the HOME environment
variable as usual. On Windows, the home directory is considered to
be the user's My Documents directory if it exists, or else the
Personal directory. These directories are found by calling
special-windows-directory with the
keywords :my-documents and
:personal.